1. Field of the Invention
This invention relates to the field of mirror optics and more particularly to the provision of an improved metal optic article comprised of an isotropic substrate of aluminum or aluminum alloy having particulate silicon carbide uniformly dispersed throughout and an optical coating which preferably has substantially similar thermal expansion characteristics to the substrate.
2. The Prior Art
Advanced optical systems find wide applications in diverse areas ranging from the cryogenic environment found in space to the physically stressful conditions to which a combat tank is subjected, from high energy laser optics to stellar telescopes. In the design of such systems, careful consideration must be given to a number of factors including cost, desirability, stability, reflectance, and the like. See, for example, "Some Fundamentals of Metal Mirrors" by William Caithness, p. B-11, SPIE Vol. 65 (1975) Metal Optics, "Basic Properties of Metal Optics" by William B. Barnes, Jr. p. 320-323, OPtical Engineering, Vol. 16, No. 4, July-August 1977, "Selection of Materials and Processes for Metal Optics" by Roger A. Paquin, p. 12-19, SPIE Vol. 65 (1975) Metal Optics, and the like.
For many applications of mirror optics it is essential that the mirror exhibit an extremely high degree of dimensional stability even, for example, under conditions of repetitive thermal cycling at extreme temperatures.
Materials used in certain mirror optic devices have of necessity been extremely costly and in certain instances have been composed of materials such as beryllium which, in addition to being extremely costly, are also severely toxic and difficult to handle safely. Workers in the mirror optics field have long sought acceptable alternative materials for use in special applications where particular properties of stability and the like are essential.
It has been taught in the prior art that metals such as aluminum and alloys of aluminum can be strengthened and reinforced by incorporating in the aluminum or aluminum alloy particles or whiskers of non-metallic materials such as silicon carbide, boron nitride, carbon and the like. The resulting materials or composites comprise a continuous metal phase of matrix with the added particles distributed throughout.
U.S. Pat. No. 3,037,857 describes aluminum base alloys having refractory metal boride particles distributed throughout. U.S. Pat. No. 2,840,891 shows aluminum and alloys thereof having various finely divided particles distributed throughout including silicon carbide, various borides, oxides, titanates and the like.
An article entitled "Theoretical and Experimental Elastic Properties of Isotropic and Transversely Isotropic Silicon Carbide/Aluminum Composites" by Dennis Regis et al was presented January 1981 at the Third Silicon Carbide/Aluminum Technology Meeting in Boulder, Colo. and describes composites of silicon carbide in aluminum.
U.S. Pat. No. 3,421,862 describes incorporation of whiskers of various materials in aluminum alloy matrices. U.S. Pat. No. 3,728,108 also describes the preparation of composites of metal alloys containing filaments or particles as does U.S. Pat. No. 3,885,959. Fiber reinforced aluminum alloys are shown also in U.S. Pat. Nos. 4,452,865, 3,441,392, 4,060,412 and 4,463,058 while the preparation of whiskers such as those of silicon carbide are shown in U.S. Pat. Nos. 4,536,379, 4,534,948 and 3,758,672.
The use of fibers such as those of silicon carbide in glass-ceramic composite substrates to which mirror surfaces are bonded are described in U.S. Pat. No. 4,554,198.